Sealed packaging unit with tear string

ABSTRACT

A packaging unit made of thermoplastic material or paper, cardboard, etc. coated with such material and which includes a container having an opening and a lid covering said opening. The lid, having peripheral drainage holes therethrough is placed in the opening on one or more support surfaces on the container walls. The container rim encircling the opening is folded over and fused into consolidation with the peripheral portion of the lid to form a hermetical seal. A tear string may be provided about the periphery of the lid.

United States Patent Gustav Sigord Barreman Mogard, Finspang, Sweden 779,547

Nov. 27, 1968 Sept. 14, 1971 Forvaltnings Aktienbolaget Acta Bromma, Sweden Dec. 6, 1967 Sweden Inventor Appl. No. Filed Patented Assignee Priority SEALED PACKAGING UNIT WITH TEAR STRING 2 Claims, 12 Drawing Figs.

US. Cl 229/51 S, 53/39, 53/329, 220/49, 229/3.5, 229/4.5, 229/5.5, 229/DIG. l4, B65d/l7/20 Int. Cl 365d 17/14, B65b 7/28, B65b 51/14 Field of Search 229/51 S,

5.5, 5.8, 3.5, 4.5, DIG. 14; 220/49 [56] References Cited UNITED STATES PATENTS 3,369,726 2/1968 Wilcox 229/5.5 3,362,571 1/1968 Kuhne.... 229/51 S X 2,642,911 6/1953 De Shazor. 229/5.5 X 2,120,899 6/1938 Moore 229/4.5 X 2,106,738 2/1938 Harrison 229/5-.5 UX 1,992,182 2/1935 Buist 229/4.5 1,678,330 7/1928 Clyne 229/5.8 X 916,485 3/1909 Porter 229/51 S 790,967 5/1905 Moxham 229/5.5 UX 3,113,689 12/1963 Moussong 217/27 Primary Examiner-Leonard Summer Att0rneyYoung & Thompson ABSTRACT: A packaging unit made of thermoplastic material or paper, cardboard, etc. coated with such material and which includes a container having an opening and a lid covering said opening. The lid, having peripheral drainage holes therethrough is placed in the opening on one or more support surfaces on the container walls. The container rim encircling the opening is folded over and fused into consolidation with the peripheral portion of the lid to form a hermetical seal. A tear string may be provided about the periphery of the lid.

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PATENTEDSEPMIBYI 3504615 SHEET 1 BF 2 y n? (j -W PATENTEUSEPMIBTI 3504.615

SHEET 2 [IF 2 INVEN TOR.

GUST/1 v 6'1 sun 46/) RREMAA/ SEALED PACKAGING UNIT WITH TEAR STRING The invention is concerned with packaging units comprising a container provided with a lid which covers the opening of said container and hermetically seals'the same and is primarily concerned with a novel type of preserving can. The invention is also concerned with a method of hermetically sealing such a packaging unit and an apparatus for carrying out the method.

In conventional preserving cans made of sheet metal the lid is attached to the container portion either by seaming or also by soldering methods wherewith a metal different to that of the container portion and the lid is used to join these two components.

Both of these sealing methods have the common disadvantage of requiring relatively complicated mechanical equipment of restricted capacity, and hence packeting costs within the preserving industry have hitherto been quite considerable. Other disadvantages associated with the two aforementioned sealing methods are that firstly it is difficult to-obtairi the correct proportioning of a liquid content of a can, andsecondly it is also difficult to avoid air from becoming trapped between the bottom of the lid and the content of the can; the oxygen content of the trapped air normally acting deleteriously on the contents of the can.

When opening conventional tin preserving cans it is almost always necessary to employ extra auxiliary means in the form of can openers, keys, perforators or the like. Consequently therexis ever present the risk of cutting the hands or fingers etc. when handling tin packaging units as well as the constant possibility of obtaining metallic impurities in the contents of the can when opening the same. Furthermore, it is normally inadvisable to store foodstuffs for any length of time in an opened preserving can which ismade of sheet metal.

In addition to packaging units made-f sheet metal, packaging units of the type defined in the introduction are also to be found which are made of thermoplastic-material and to which the lid is joined bymeans of heat. These packaging units, however, are primarily intended for diary products and because of their-design which generally includes an outwardly projecting side flange unsuitable for preserving cans have not found use within the preserving industry.

The object of the present invention is to eliminate the aforementioned disadvantages and is also intended to lower the costs of transporting such containers and to reduce checking of the packaging units subsequent to their being sealed.

These objects and purposes are achieved by means of the invention which primarily concernsa packaging unit of the type defined inthe 'in troduction and with which thelid is joined to the containerin'a known mannerby means of heat, primarily by placing the lid of a packaging unit designed in accordance with the invention in the container opening where it rests against one or more support surfaces on the walls of the container, and in which the'edges of the container surrounding the opening are folded in over the circumferential portion of the lid and fused and consolidated together therewith; In a packaging unit of this type'the container portion and the lid may be made either completely of thermoplastic material or of paper, cardboard or the like coated with such a material. Because all of these materials are lighter than sheet-metal the costs of transporting said units are reduced to a corresponding, extent. Simultaneously, folding of the edges of the container walls over the circumferential portion of the lid and the welding together of said lid and container is a simple operation which, in comparison with seaming or soldering operations in the case of packaging units made of sheet metal, can be effected with relatively simple equipment which is inexpensive to operate and with appreciably reduced post checking of the completed packaging units, which because the lid and container are fused and consolidated together comprise units made of one and the same material.

In a particularly advantageous embodiment of a packaging unit designed according to the invention the supportsurfaces on the container walls consist of a shoulder which extends along the walls of the container and is formed in the material of said wall. In addition to constituting a lid support surface, the shoulder also serves as a distance member determining the used volume of the can. It is also possible to utilize the upper end surfaces of a number of reinforcing and distance ribs as the aforementioned support surfaces, the said ribs being formed in the material of the wall and spaced around the same and made to extend out along the walls from the bottom of the container towards the opening thereof. The use of reinforcing ribs, which also function as distance members in determining the utilizedheight of the can, enables the container to be made with very thin walls, which adds to the lightness of the packaging unit. The ribs provide the requisite rigidity of the walls. H

In order to provide the packaging unit with a shape-retaining stiffness already when the lid is placed in the container opening and at the same time to provide the lid with the best possible support from the support surface or surfaces it is possible, according to one embodiment of the invention, to incline the support surface or surfaces outwardly and downwardly towards the defining container wall and to provide a reinforcing flange on the inside of the lid, adjacent to its periphery, wherewith at least a portion of the underneath of said flange is conformingly chamfered or inclined for abutment with the aforementioned sloping support surface or surfaces.

If desired, both the lid and the bottom of the container can be reinforced in a known manner by means of a dome, circular orradial raised portions or the like, said reinforcements being formed in the material of the lid and the container respectivelyplf radial projections are provided on the bottom of the container said projections are suitably formed as continuations of the reinforcing and distance ribs which extend along the container walls from the. bottom of the container towards the container opening. In order to provide a suitable quantity of material in the peripheral portion of the lid to enable the folded wall edges of the container to be fused and consolidated with the lid, a reinforcing flange is conveniently arranged on the outside of the lid adjacent its periphery, said flange in the case of a hermetically sealed packaging unit being fused and consolidated with the inwardly folded edges of the container wallsi' The disadvantage and risks entailed when opening a conventional preserving can made of sheet metal are completely eliminated in a packaging unit manufactured in accordance with the invention since, for instance,.it can be opened in a particularly simple manner by pulling a wire thread or cord which is grouted in the lid and at least one end of which constitutes a gripping means located outside the lid. When opening the packaging unit, the wire or string cuts through the material around the edges of the lid to expose the contents of said unit. Because thematerial from which the packaging un it is made does not give rise to cutting surfaces when torn, there is no risk of cutting the hands etc. when opening the packaging unit.

In accordance with another feature of the invention, a correct and automatic -proportioning of liquid content of a packaging unit is obtained by providing the lid of the packaging unit according to the invention with a number of drainage 1 openings in the proximity of the periphery thereof which allow excess liquid content to flow out of the container when the lid is placed on the support surface or surfaces in the opening thereof. Furthermore, the drainage openings prevent air from remaining under the lid since all air is ejected together with the excess contents of the can. For this purpose, the lid may be given a concave shape so that air trapped beneath the same is forced to move towards the drainage holes. To counteract the occurrence of air bubbles on the under surface of the lid it is suitable to shake the packaging unit before hermetically sealing the same to .cause the bubbles to move towards the drainage holes through which the air can then escape. When the packaging unit is sealed hermetically the drainage holes are automatically closed as the edges of the container wall are folded over and welded together with the peripheral portion of the lid.

To facilitate sealing of the packaging unit according to the invention, which should naturally be effected with equipment which is automated to the highest possible degree, the opposing edge portions of the container may suitably be caused to diverge towards the bottom of the container, whereby the packaging unit obtains a downwardly tapering shape.

Because the packaging unit according to the invention can either be made wholly of a plastic material or of a plasticcoated material, the advantage is gained with respect to conventional metal preserving cans that the contents can remain in an opened packaging unit for a longer period of time without going bad. Consequently, after its original use the packagingtunit according to the invention can be cleaned and used for storing foodstuffs etc. and is exceptionally well suited for use as a deep-freeze packaging unit subsequent to being provided with a suitable, separate lid. The intention is also to manufacture and retail such lids.

A packaging unit made according to the invention can be used both for semipreserved goods, where sterilizing is not required, and for fully preserved goods, where sterilizing is required. Owing to the fact that the packaging material cannot withstand high temperatures, sterilizing is effected in an electric oven which emits so-called cold heat. These ovens should be provided with different pressure sections to counteract any overpressure which might occur during the actual sterilizing process.

If the pressure in the packaging unit is to be lower than the atmospheric pressure, the lid should be provided with an evacuation pipe or the like through which the air pressure inside the packaging unit can be lowered whereafter the pipe or the like is fused and clipped off, preferably in one and the same step.

As mentioned in the aforegoing, the invention is also concerned with a method of hermetically sealing a packaging unit of the type mentioned above consisting of a container and a lid covering the opening thereof. The method is mainly characterized in that the container is placed in a device or fixture which embraces said container and fixes its position, that the lid is placed in the container opening into abutment with the support surface or surfaces, and that the edges surrounding the opening of the container walls are folded over and fused together with the peripheral portion of the lid by means of heat.

In order to protect the packaging unit when sealing against excess heat, the center portion of the lid can suitably be cooled with air or water. It is also suitable to move the packaging unit axially in the surrounding fixture when heat is applied to the edges of the container and the peripheral portion of the lid with the heated wall edges in sliding abutment against said fixture. Together with the previously mentioned downwardly tapering shape of the packaging unit, this axial movement contributes towards providing an effective inward folding of the container wall edges over the peripheral portion of the lid.

In addition to the actual packaging unit and the method of hermetically sealing the same the invention, as previously mentioned above, is also concerned with an apparatus for carrying out the sealing method. The apparatus is mainly characterized in that it primarily includes a support means or fixture intended to fix the position of the container during the sealing process and a heat transfer means which is placed above said support means coaxial therewith and at least a part of which can be inserted into the fixture for the purpose of transferring heat to the edges of the container wall and the peripheral portion of the lid.

To facilitate both the positioning of the containers in the fixture and the removal of the sealed packaging units therefrom and to provide suitable support for the containers, the fixture is preferably designed essentially as an openable and closable sleeve or the like which is shaped to embrace the walls of the container and the height of which is at least equal to the height of the container walls before the packaging unit is sealed.

Cooling of the lid can be facilitated by providing the free end of that part of the heat transfer means which can be inserted into the fixture, in the following called the insertable part, with a cavity which is open towards the lid of the packaging unit. In other respects the insertable part of the heat transfer means should be made to conform to the flat shape and the size of the packaging unit and preferably present a wall thickness which corresponds to the width of the zone within which the wall edges of the container are folded over and fused together with the peripheral portion of the lid.

In a particularly advantageous embodiment of the apparatus according to the invention, channels for the supply and return of the cooling medium, which may be air or water or any other flowing medium suitable for the purpose, are arranged within the heat transferring device. The channels are opened towards the cavity in the insertable part of the heat transfer means and there is a protective cover mounted around the channel opening. During the sealing process the protective cover is intended to lie so that its periphery sealingly abuts the lid of the packaging unit and directs cooling medium arriving from the supply channel towards the lid but, at the same time, prevents the medium from reaching the parts of the packaging unit which are subjected to heat.

In principle the heat transfer member may be completely or partially surrounded or enclosed by one or more suitable heat emitting devices which may, for instance, be in the form of an electric jacket element.

In addition to being designed for the direct purpose of conforming to a certain shape and size of the packaging unit according to the invention, both the fixture and at least the free end of the insertable part of the heat transfer means may be composed of construction units which enable them to be adjusted to packaging units of different shapes and sizes. By systemizing said construction units, packaging units made according to the invention and being of widely different shapes and sizes can be sealed by means of the said means which is intended to operate automatically to the largest possible extent.

The invention will now be described with reference to a number of preferred embodiments of the packaging unit and the apparatus for hermetically sealing said unit, the embodiments being illustrated in the accompanying drawing in which FIG. 1 is a perspective view of a packaging unit made according to the invention, which is hermetically sealed by means of the apparatus shown in FIG. 7-9,

FIG. 2 is a plan view of the inner of the container part of the packaging unit,

FIG. 3 is a section along the line 3-3 in FIG. 2 through the container portion, '3

FIG. 4 is a plan view of the lid of the packaging unit,

FIG. 5 is a simplified section through the Iine S S in FIG. 4 ofthelid,

FIG. 5a is an enlarged scale of the section in FIG. 5 showing the details which were omitted from FIG. 5 for clarity,

FIG. 6 is an enlarged scale of a section corresponding to FIGS. 3 and 5 through the container portion and the lid, which in this Figure is placed in the container opening the lefthand portion of the Figure shows the lid loosely inserted in the opening of the container portion while the right-hand side of the Figure shows how edges surrounding the opening of the container walls are folded in over and fused and consolidated with a peripheral portion of the lid,

FIGS. 6a and 6b show in enlarged scale the section in FIG. 6

FIG. 7 is a diagrammatic plan view of an apparatus according to the invention for hermetically sealing the packaging units shown in FIGS. l6,

FIG. 8 is an axial section through the sealing apparatus shown in FIG. 7 before a packaging unit has been inserted therein for the purpose of being hermetically sealed, and

FIG. 9 is a section corresponding to FIG. 8 through the sealing apparatus subsequent to a packaging unit has been placed therein to be sealed.

The drawing shows a suitable, essentially cylindrical shape for the packaging unit of the invention intended as a preserving can or the like. A cylindrical shape has been chosen to illustrate the invention solely for the purpose of simplifying the drawings. The packaging unit of the invention may be of any shape and size, For instance, in addition to having the cylindrical shape shown, the packaging unit may be oval or square or any other preferred shape.

As shown in FIGS. 1-6, the packaging unit according to the invention comprises two parts, a container 1 and a lid 2, which covers the container opening. Both the container and the lid are preferably made of molded thermoplastic material but may also be made to advantage of, for instance, thermoplasticcoated fibrous material such as paper, cardboard, pasteboard or the like.

FIGS. 2 and 3 illustrate how the container 1 can suitably be provided with the necessary support surfaces 4 for assembling the lid 2 in the container opening. In the shown embodiment said support surfaces consist of the upper end surfaces of a number of reinforcing or distance ribs 5 disposed around the container wall and formed in the actual material of said Wall and which extend along the wall from the bottom 6 of the container towards the opening. As the name of said elements implies, the ribs fulfill a number of functions. In addition to providing a support for the lid 2 with their end surfaces, they stiffen the container walls and also determine the height of the storage space in the container. If a more rigid container wall is required, it is of course possible to increase the number of ribs 5 but it is also possible to increase the thickness of the wall.

lrrespective of whether the support surfaces 4 are in the form of a shoulder extending around the wall of the container or in the form of end surfaces of the ribs 5, they can be made to slope outwardly and downwardly towards the bordering container wall portion in the manner particularly evident from FIG. 3 so as to provide the lid with the best possible support and so that the packaging unit obtains an expedient shaperetaining stiffness from the very moment the lid is inserted in the container opening. If considered necessary, the bottom 6 of the container 1 may also be reinforced which is conveniently effected by arranging a conventional dome 7 therein or by means of known circular or radial raised portions or the like (not shown).

For reasons which will become apparent from the following, the walls of the container 1 diverge towards the bottom 6, thus imparting a certain conicity which should not be less than 1.

F 4 and 5 show the preferred design of the lid 2 for the container 1 shown in FIGS. 2 and 3. It is evident from the aforegoing that the lid 2 shall cover the opening of the container 1 when said lid is placed on the support surfaces 4. It is therefore given a diameter which corresponds to the container opening. To facilitate the abutment of the lid against the support surfaces 4, the inside of the lid is provided at the circumference thereof with a reinforcing flange 8. A portion 9 of the undersurface of the flange 8 is provided with an inclination adapted for abutment with the inclined support surfaces 4 on the ribs 5 of the container wall. A second reinforcing flange 10 is arranged on the top of the lid adjacent the circumference thereof. The flange 10 is intended to be fused and con solidated with the edge 11 encircling the opening of the container wall when said edge is folded over the peripheral portion of the lid 2 and fused together with said lid during the process of hermetically sealing the can. in addition to the two special reinforcing flanges 8 and 10 the lid 2, as in the case of the bottom 6, may of course be provided with a dome or circular or radial raised portions or the like, formed in the actual material of the lid. No such stiffening means are employed, however, on the lid shown in the drawings.

As will be especially evident from FIGS. 4 and 5, the lid is provided with penetrating drainage holes 12 which permits automatic proportioning of a liquid content of the can when the lid is placed on the support surfaces 4 in the opening. The holes 12 are dispersed around the lid in the vicinity of the periphery thereof to be sealed when hermetically sealing the can by the container edge 11 when it is folded over the peripheral portion of the lid 2 and fused and consolidated therewith. in the case of the lid of the illustrative embodiment,

the holes 12 are arranged in the bottom of a groove 14 which is intended to accommodate a tear wire or string 13. The groove 14 is placed in the flange 8 on the inside of the lid where for obvious reasons it is preferably situated behind the portion 9 of the underneath of the flange which presents an inclined surface adapted for abutment with the inclined sup port surfaces 4.

The tear wire or string 13 may be attached to the lid 2 in a number of ways, of which only one has been illustrated and may be made of stainless steel or some other suitable material. As the name implies, the element 13 is intended to facilitate opening of the packaging unit, and in the illustrative embodiment is shown already mounted in groove 14 in lid 2 when this is placed in the container opening. The groove 14 and wire 13 extend around the larger portion of the lid to enable the contents of the can to be reached easily when said can is opened by means of the wire. The portion 15 of the lid, FIG. 1, which is not cut by the wire when the can is opened is sufficiently large to form a hinge for the lid and to permit the lid to be removed from the container 1 easily. The two ends 16,17 of the wire 13 extend out from the outside of the lid and at least one end 16 is long enough to provide sufiicient grip when opening the can while the other 17 need only be bent down, for instance, to prevent the wire from sliding in groove 14 instead of tearing the lid 2. The end 16 of wire 13 may also be provided with some suitable form of gripping means such as a loop or the like and the end 17 may be made thicker or be knotted etc.

When applying the method of the invention to seal hermetically the packaging unit shown in FIGS. 1-6, the lid 2 is placed in the container opening where, as can be seen in FIG. 6 and partly in FIG. 6a, said lid rests with the flange portion 9 against support surfaces 4 on the ribs 5. The edge 11 encircling the opening of the container wall is then folded over and fused with the peripheral portion of the lid and the flange 10 within said peripheral portion on top of the lid as can be seen from the right-hand side of FIG. 6 and from FIG. 6a. The process of fusing and consolidating together these elements gives rise to an annular raised portion 18 extending around the circumference of the top of the packaging unit whereupon it should be seen that said raised portion is of such form that the units can be safely stacked, one on top of the other. It is also possible to provide the bottom of the cans with a similar annular raised portion to improve further the possibility of stacking the cans.

FIGS. 7-9 show an apparatus for hermetically sealing the packaging unit illustrated in FIGS. 1-6 and which in accordance with the invention consists essentially of a support means 20 intended for fixing the position of the container 1 during the sealing process, and a heat transfer means 21 arranged axially above said means 20. Heat is transmitted by the heat transfer means 21 of which at least part 22. can be inserted into the support means or fixture 20 to the edge of the container wall and the peripheral portion of the lid to fuse and consolidate said elements together.

When sealing the packaging unit, the unit is passed into the support means or fixture 20, suitably by means of an automatically operating conveyor system, and the lid placed in the opening of the container whereupon the part 22 of the heat transfer means 21, which can be inserted into the support means 20, is brought into contact with container wall 11 to heat said wall and fold the same over the contemporaneously heated peripheral portion of the lid to be fused and consolidated therewith. Subsequent to the completion of the sealing process, the sealed packaging unit is removed from the fixture 20.

To facilitate the insertion and removal of the can into and out of the fixture 20, the fixture can be designed to be opened and closed and is for this purpose divided into two halves 23 and 24 which when brought together form a sleeve around the container portion 1. The dimensions of the sleeve should be such to allow an axial movement of some few millimeters of the container in the sleeve when heat is applied to the edge 11 of the wall and the peripheral portion of the lid. During this movement the hot edge is in sliding contact with the wall of the sleeve; it is for this purpose the walls of the containerare made to converge towards the bottom of the container. The axial displacement of the container in the sleeve is intended to contribute towards effective folding of the edge 11 over the peripheral portion of the lid 2.

In the illustrated embodiment of the sealing apparatus of the invention, the part 22 of the heat transfer means 21,.which can be inserted in the fixture 20, is annular in shape and made in one piece and is adapted in shape and size to the packaging unit shown in FIGS. 1-6. in the case of oval or square, for instance, packaging units, the shape and size of the part 22 must be changed accordingly. The means 21 and part 22 are suitably made of copper. By composing the insertable part 22 of means 21 of units (not shown) systemized with regard to shape and size, the said part 22 can readily be modified to fit packaging units of varying shapes and sizes. Similarly, the fixture can also be composed of systemized units (not shown). in the shown embodiment the insertable part 20 of t he heat transfer means is fitted to the lower end of a copper sleeve 25 which is adapted in some suitable manner to be moved vertically and secured to said sleeve by means of bolts 26, for example. The sleeve is encircled above the exchangeable part 22 by an electric jacket element 27 which is only shown diagrammatically in the Figures. The jacket element 27 is preferably controlled by a thermostat.

Arranged inside the sleeve 25, one within the other, are two tubes 28 and 29. As can be seen from FIG. 7 each of the tubes is connected at the top with a hose, pipe or the like 30 and 31 respectively. Water, air or some other suitable coolant is passed through the hose or pipe 31 and the tube 2? to the interior of a funnel shaped protective cover 32 which is suitably attached to the bottom of tube 28 and which through the intermediary of a heat resistant seal 33 located at the bottom edge of said cover abuts the outside of the lid 2 during the sealing procedure. The funnel shaped protective cover 32 is provided at the top thereof with a number of holes 34 arranged in a circle to connect the interior of the cover 32 with the annular passage 35 formed between the tubes 28 and 29,

the bottom of said passage 35 being closed by the annular portion of cover 32 in which the holes 34 are disposed.

Subsequent to contacting the portion of the lid 2 enclosed in the protective cover 32, the coolant is returned through holes 34 to the annular passage 35 which thus constitutes a return channel for the coolant. As is evident from the arrows in FIG. 9, the cover 32 directs the coolant arriving from the supply channels 31,29 towards the lid 2 simultaneously as it prevents the medium from reaching those portions of the packaging unit which are subjected to heat and ensures that the coolant is returned through the holes 34 to the return channel 35.

In addition to it being possible to design a packaging unit of the type described in a plurality of different ways (which have not been shown) without digressing from the concept of the invention, the sealing apparatus and its different components can also be designed differently. For instance, cooling can be effected by spraying cooling water freely over the packaging unit whereby the unit is cleaned at the same time. Similarly the insertable part of the heat transfer means can be designed so that its surfaces which come into contact with the packaging unit contribute directly to the step of folding the edges of the container walls over the peripheral portion of the lid.

What I claim is:

1. A packaging unit comprising a container having an opening and a lid covering said opening, said lid being placed in said opening on at least one support surface on the container walls, the edges of the container walls which encircle said opening being folded over and fused into consolidation with the peripheral portion of said lid to form a hermetical seal, said lid having drainage holes therethrough in the vicinity of its periphery, said holes being closed by said edges of said container walls folded over said peripheral portion of said lid and fused and consolidated therewith.

2. A packaging unit as claimed in claim 1, said lid having a downwardly opening groove about the periphery of the underside thereof, string means disposed in said groove and extending outside the packaging unit to be grasped and pulled to sever the lid, said drainage holes opening downwardly into the bottom of said groove. 

1. A packaging unit comprising a container having an opening and a lid covering said opening, said lid being placed in said opening on at least one support surface on the container walls, the edges of the container walls which encircle said opening being folded over and fused into consolidation with the peripheral portion of said lid to form a hermetical seal, said lid having drainage holes therethrough in the vicinity of its periphery, said holes being closed by said edges of said container walls folded over said peripheral portion of said lid and fused and consolidated therewith.
 2. A packaging unit as claimed in claim 1, said lid having a downwardly opening groove about the periphery of the underside thereof, string means disposed in said groove and extending outside the packaging unit to be grasped and pulled to sever the lid, said drainage holes opening downwardly into the bottom of said groove. 